Hi Charles!
What a wonderful instrument! A great choice of subject.
Congrats on the picture. The wood is rich and beautiful and the shape has movement. One might have added a background. You still could, but I find that negative space to be interesting and allow the mind to ask questions about what one's seeing and what it might mean.
I really like the lines of the mandolin, as it is reminiscent of other things like boats that might have sailed the Mediterranean or around Turkey, trading spices, wines and grain.
In fact, I could imagine a dark water background. But that is not needed, as the picture is, itself, impressive. No doubt, someone else might ask for some verticals to complete the composition. I would argue that starkness is part of its impact.
If any of that is what you intended then I have understood you. Otherwise, chalk it down to my own romanticism and distractibility by beautiful things.
Although I love this image as is and would be proud to see it on my wall, I presume you are going to do a lot more with shading using different lighting. You could in fact, work on just this for the next month. This is a superb and really challenging thing to photograph and I think you have only just touched the very surface of all the richness you will get with further work.
A series, just of this comes to mind.
Asher